The overall objectives are: To determine whether prostaglandins (PGs) act DIRECTLY upon luteal tissue (or only indirectly). Organ cultures containing corpora lutea will be subjects in most of the experiments. To develop an organ culture assay system for untried substances with potential luteolytic activity. To add insight into the mechanisms responsible for luteolysis by studies upon corpus luteum in organ culture. To understand better the properties of luteal tissue at the molecular and cellular level. To add insight into the mode of action of PGs on uterus. To determine whether PGs DIRECTLY render uterus more responsive or less responsive to estrogen and progestin. This could contribute to our knowledge of uterine contractility mechanisms and control of the initiation of or interference with ovoimplanatation and placentation. The specific aims are to investigate: (in ovary cultures) 1) The direct effect of PGs on luteal cells in organ culture; to determine whether PGs promote luteolysis by direct action on luteal tissue. 2) The direct effect of PGs on the synthesis of steroid hormones by the corpus luteum in organ culture. To determine whether PGs can cause biochemical lesions that interfere with normal synthetic pathways in corpus luteum. To determine whether PGs can augment steroidogenesis in cultured corpus luteum. 3) The direct effects of PGs on lysosomal activity, glucose utilization, and oxygen consumption of the corpus luteum in organ culture; (In uterus cultures) 4) The direct effects of PGs on the uptake of progesterone and estradiol by uterine organ cultures. 5) The direct effects of PGs on the levels of hormone receptor protein of the uterus in organ culture.